_____PbS+_____O3=________PbSO4+____O2这个配平我配1211,而答案是1414,为什么我的是错的?

_____PbS+_____O3=________PbSO4+____O2这个配平我配1211,而答案是1414,为什么我的是错的? return from=___ ___ ___? The girl is good at singing.=___ ___ girl ___ ___ good at singing.=___ ___ ___girl ___ ___ ___.还=___ ___ girl ___ ___ ___ ___ singing. 英语翻译My sister is ___ ___ working in that company.=My sister ___ ___ ___ ___ ___ ___ ___ ___. He said,I lost my pen yesterday.=He said that ___ ___ ___ ___ pen ___ ___ ___. 给下面单词加一个字母ear+___=___ hat+___=___ us+___=___ our+___=___and+___=___ now+___=___ each+___=___ Kitty came here three years ago=It ___ ___ ___ ___ since Kitty __ ___ 2n+7n=(___+___)n=___ 数学题求答案!速度!年利率=___×12,利息=___×___×___,利息税=___×___税后利息=___×（1-___）,本利和=___+___税后本利和=___+___ 几道有理数加减法的填空题.（-20）+（+3）-（-5）-（+7）=___+___+___+___=___=___；(+9)-(+10)+(-2)-(-8)+2=___+___+___+___+___=___. 81.21°=___度___分___秒 数学题10.12°=___°___'___ 33.52°=___度___分___秒 the room is tidy =it is ___ ___ ___ to tell you the true=___ ___ ___ 39.145°=___度___分___秒 pretty healthy= ___ ___ ___(填3个词) 英语翻译It is ___ ___ to travel ___ ___ ___ ___.注意后面是四个空,咋填 = =